[howardjones]

Hello. I could use help G76 programming the threads mentioned above on a cnc lathe with fanuc controls. Material is 86L20. Threads are 1.5 long. I have never done anything like this and would definitely appreciate help. Thanks.

[howardjones]

Hello. I could use help G76 programming the threads mentioned above on a cnc lathe with fanuc controls. Material is 86L20. Threads are 1.5 long. I have never done anything like this and would definitely appreciate help. Thanks.

They are external threads

[Jim Dawson]

Most CAM programs will generate the G code to do exactly what you want. The Z start point is offset for the second lead. You just need to make sure that you are using the correct tool profile so there is proper clearance.

If you can use a G32 cycle, it is more adaptable.

[howardjones]

Thanks for reply Jim. How far out would I move Z starting point for second G76 pass to make the threads double lead? Still confused. This part has me stumped. I have cut acme threads before but never external acme stubs with double lead.

[Jim Dawson]

Thanks for reply Jim. How far out would I move Z starting point for second G76 pass to make the threads double lead? Still confused. This part has me stumped. I have cut acme threads before but never external acme stubs with double lead.

I let the CAM program figure that out. But I think it would 1/2 the lead. That should allow the spindle to make 1/2 rotation extra before the tool engages the work, so the start would be 180° from the first start.